1. Field of the Invention
The present invention relates to vehicle control systems for controlling charging and discharging of a battery, mounted to vehicles such as passenger vehicles and trucks, based on temperature characteristics of the battery and for controlling electric-power generation condition of a vehicle alternator based on battery conditions such as a temperature of the battery.
2. Description of the Related Art
Recently, the reduction of carbon dioxide (CO2) is strongly demanded for prevention of global warming. Achieving this demand needs the improvement of fuel consumption for passenger vehicles and trucks. This is also a strong demand in the automobile industry field.
Conventional techniques have proposed various methods to improve the fuel consumption of vehicles based on controlling the charging of an on-vehicle battery using more-detailed information about the condition of an on-vehicle battery. For example, one conventional method controls the battery charging operation, and reduces a load of the engine of a vehicle when the vehicle is accelerated. The conventional method also increases the amount of electric energy, to be charged to the on-vehicle battery, using regenerated energy obtained when the vehicle is decelerated. That control is a well-known technique. Such a vehicle is equipped with a current sensor in order to precisely monitor the charging and discharging balance of the on-vehicle battery.
By the way, the charging and discharging characteristics of a lead battery mounted to a vehicle fluctuates according to the chemical reaction state of the lead battery. In particular, the charging condition greatly fluctuates according to the temperature of the lead battery, namely, at a high temperature and a low temperature. This means there is a necessity to accurately control the charging voltage for the lead battery based on its temperature. Not controlling the charging voltage based on the temperature of a lead battery will cause a poor charged state of the lead battery at a low temperature, and also cause an over charged state thereof at a high temperature.
In order to avoid this problem, a conventional technique controls the charging and discharging operation for the lead battery based on an estimated temperature of the lead battery. For example, Japanese patent laid open publication No. JP H10-215527 has disclosed such a conventional technique. However, the conventional technique JP H10-215527 performs the charging and discharging control based on the estimated temperature of the battery with relatively a low accuracy. It is accordingly difficult for the conventional technique to perform the charging and discharging control for the battery with more accuracy from the viewpoint of fuel consumption improvement. Still further, the conventional technique JP H10-215527 limits the space for the battery to be mounted to the vehicle.
Recently, various types of devices that purify exhaust gas and improve the fuel consumption of a vehicle are mounted into the engine room of the vehicle in addition to the battery. This limits the mounting space for the battery or largely changes the mounting location of the battery in the engine room of the vehicle. For example, there is a case to mount the battery into a trunk room of the vehicle. This also causes various problems.